In vehicle construction, motor vehicle steering column units are installed in passenger cars and trucks. The general design of such units is characterized in that there is a section that can be telescoped and tilted for each direction of adjustment (longitudinal adjustment and tilt adjustment), and each section can be activated by the user via a coupling and an adjustment in the corresponding direction can thus be performed.
Such a steering column unit is disclosed in patent DE 196 41 152 C2 and shown in attached FIGS. 4 and 5. It comprises a steering column housing 14, a steering column 15 arranged therein, and an electrically driven adjusting device for the longitudinal adjustment and for the tilt adjustment of the steering column 15. The adjusting device comprises an electric motor 17, which rotates a one-part adjusting spindle 18, as well as two spindle nuts 19 in a respective bearing housing 16, which said spindle nuts are mounted movably in the axial direction of the adjusting spindle 18. An adjusting mechanism (connecting lever 20, tilting lever 21) as well as a switching device 22 (lifting magnet) each are provided for the longitudinal movement and for the tilting movement, and a temporary rigid connection is established by the user between the respective adjusting device 22 and the spindle nut 24 corresponding to the switching device 22 during the adjustment. The respective spindle nut 19 forms a so-called adjusting unit with the respective bearing housing 16 and the respective switching device 22. An adjusting unit, which has a switching device 22 (for example, a lifting magnet), will be called a coupling in the further course of the specification.
The mode of operation of the adjusting mechanism is explained in greater detail on the basis of FIG. 5. The adjusting spindle 18, which is driven at one of its ends by an electric motor (not shown in FIG. 5), is shown in an axial sectional view. Two thrust bearings 23, in which a spindle nut 24 each is mounted, are located at a defined distance from one another. The internal thread of one spindle nut 24 corresponds to the external thread of the adjusting spindle 18. The moment of friction between the adjusting spindle 18 and the spindle nut 24 is greater than the moment of friction between the spindle nut 24 and the thrust bearing 23, so that a rotary movement of the adjusting spindle 18 brings about rotary movements of both spindle nuts 24 in the same direction without a change taking place in the position of the thrust bearings 23 with the spindle nuts 24 contained therein in the axial longitudinal direction. The right-hand adjusting unit is provided with a switching device 22, which is a lifting magnet in this exemplary embodiment. This lifting magnet 22 has a pin 25, which can be extended from the lifting magnet housing in the direction of the central axis of the adjusting spindle 18 during the actuation of the lifting magnet 22 and engages an opening 26 of the spindle nut 24. As a result, a rigid mechanical connection is brought about by the switching device 22 (lifting magnet) between the thrust bearing 23 and the spindle nut 24, so that the rotary movement of the spindle nut 24 is blocked and the rotation of the adjusting spindle 18 inevitably leads to an axial displacement of the spindle nut 24. This axial displacement is converted by a suitable mechanism (by means of the connecting lever 20 and the tilting lever 21) into an axial displacement or tilting of the steering column housing 14.
In a steering column of the above-described design and possessing the above-mentioned properties, the direction of adjustment can be selected by actuating the corresponding adjusting unit or coupling.